Partial rescue of defects in Cited2-deficient embryos by HIF-1α heterozygosity

Abstract

Hypoxia inducible factor-1 (HIF-1) initiates key cellular and tissue responses to physiological and pathological hypoxia. Evidence from in vitro and structural analyses supports a critical role for Cited2 in down-regulating HIF-1-mediated transcription by competing for binding with oxygen-sensitive HIF-1alpha to transcriptional co-activators CBP/p300. We previously detected elevated expression of HIF-1 target genes in Cited2(-/-) embryonic hearts, indicating that Cited2 inhibits HIF-1 transactivation in vivo. In this study, we show for the first time that highly hypoxic cardiac regions in mouse embryos corresponded to the sites of defects in Cited2(-/-) embryos and that defects of the outflow tract, interventricular septum, cardiac vasculature, and hyposplenia were largely rescued by HIF-1alpha haploinsufficiency. The hypoxia of the outflow tract and interventricular septum peaked at E13.5 and dissipated by E15.5 in wild-type hearts, but persisted in E15.5 Cited2(-/-) hearts. The persistent hypoxia and abnormal vasculature in the myocardium of interventricular septum in E15.5 Cited2(-/-) hearts were rescued with decreased HIF-1alpha gene dosage. Accordingly, mRNA levels of HIF-1-responsive genes were reduced in Cited2(-/-) embryonic hearts by HIF-1alpha heterozygosity. These findings suggest that a precise level of HIF-1 transcriptional activity critical for normal development is triggered by differential hypoxia and regulated through feedback inhibition by Cited2.

Cited2, a Transcriptional Modulator Protein, Regulates Metabolism in Murine Embryonic Stem Cells

“…The appearance of the mesoderm marker T gene after a HIF-1␣ knockdown in Cited2-deleted ESCs is also consistent with our previous study that HIF-1␣ down-regulation can partially rescue the defects in cardiac development (52). Our finding that dysregulated expression of pluripotency marker Oct4, epiblast marker Fgf5, and trophoectoderm marker Cdx2 in Cited2 ⌬/Ϫ EBs was not corrected by HIF-1␣ knockdown suggests several possibilities.…”

“…Cited2 competes with HIF-1␣ in binding to the CH1 domain of CBP/p300 and thus modulates key biological functions in heart, eye, and hematopoietic stem cells (8,(52)(53)(54). HIF-1 is responsible for controlling the rate of glycolysis in ESC lines with gain-or loss-of-function of HIF-1␣.…”

Cited2 is required for normal hematopoiesis in the murine fetal liver

“…41 Up-regulated HIF-1 signaling is observed in Cited2-deficient embryonic hearts and has been shown to be partially responsible for the defective heart morphogenesis due to Cited2 deficiency. 8,13 However, Cited2-deficient fetal liver manifested multiple lineage hematopoietic defects during development, which could not be explained by dysregulated HIF-1 signaling alone based on the known functions of HIF family members in hematopoiesis and the negative regulatory role of Cited2 in HIF-1-mediated responses revealed by other studies. 8,39,40 Hypoxia also promotes the undifferentiated cell state in various stem and precursor cell types, and Notch signaling has been shown to be in part responsible for hypoxia-mediated processes in myogenic and neuronal precursor cells.…”

“…Deletion of Cited2 gene results in embryonic lethality in the mid to late gestation with embryos displaying cardiac malformations, neural tube defects, 7 adrenal agenesis, [8][9][10] left-right patterning defects, 9,11 and placental defects. 12 Further mechanistic studies have provided evidence that Cited2 plays pivotal roles in these processes through its transcriptional modulator functions for HIF-1 8,13 or AP-2␣ signaling. [9][10][11] Accumulated evidence has implicated the role of Cited2 in hematopoiesis because Bmi-1, which is essential for adult hematopoietic stem cell self-renewal, 14 is induced by Cited2 in mouse embryonic fibroblast (MEF) cells.…”

Developmental regulation of hypoxia-inducible factor 1 and prolyl-hydroxylases in pulmonary vascular smooth muscle cells

“…Similar to PHD2 and FIH, CITED2 activation by hypoxia might indicate a role for this molecule in the rapid inactivation of the hypoxic response upon reoxygenation. CITED2 may play a role in heart morphogenesis and the establishment of left-right asymmetry in the early embryo (20)(21)(22).…”